Installation for electroslag remelting of consumable electrodes

ABSTRACT

An installation for the electroslag remelting of consumable metal electrodes in a cooled mold, wherein a current supply means is provided to supply working electrical current to melt the electrode and wherein short impulses of current are impressed upon this working current. The amplitude and duration of the short current pulses are sufficient to effect positive breaking off of drops of the electrode metal during the formation of the drops prior to the time at which they would naturally drop.

United States Patent Paton et al. 51 May 23,1972

[ INSTALLATION FOR ELECTROSLAG R r n s Cited REMELTING OF CONSUMABLE UNITED STATES PATENTS ELECTRODES 3,193,605 7/l965 Dreyfus ..l3/l2 1 Inventors: Boris Evzentevlch Pawn; Boris lmilevich 3,469,968 9/1969 Snow ..13/9 x Medovar; Oleg Petrovich Bondarenko; Jury Vadimovich Latash; Vitaly Mik- Pn-ma d ry ,xammer mar A. Gllheany haflovlch i vhdimir Gngm'ievich Assistant Examiner-R. N. Envall, Jr. shirshov of Kiev Attomey-Waters, Roditi, Schwartz & Nissen [22] Filed: Mar. 10, 1970 57 ABSTRACT [21] Appl. No.2 23,112 1 An installation for the electroslag remelting of consumable R l l 1 pp i a io Dim metal electrodes in a cooled mold, wherein a current supply I 62] Division of Sen No 644 719 June 8 1967 which is a means is provided to supply working electrical current to melt Continuation of Ser No 4 18 l'970 the electrode and wherein short impulses of current are im- V .3..-" .L.MLW.; pressed upon this working current. The amplitude and dura- 52] us 0 "13/9 13/12 tion of the short current pulses are sufficient to effect positive 5 1] Int CL 3, 3/60 breaking off of drops of the electrode metal during the forma- 58 Field of Search ..19 9, 12 P Prior the time which they wuld rally drop.

8 Claims, 6 Drawing Figures PATENTEDmza I972 3, 665,488

SHLU 2 OF 2 p] 4 a Q M 92 F163 73 A v ll it. 4% y L 6 My :97. I) J q INVEN'I'OR BORIS E. PATON, e? cl.

INSTALLATION FOR ELECTROSLAG REMELTING OF CONSUMABLE ELECTRODES This application is a division of copending application Ser. No. 644,719, filed June 8, 1967, which was replaced by continuation application Ser. No. 64,825, filed Aug. 18, 1970.

The present invention relates to installations for slag remelting of consumable electrodes.

The invention is intended to be used in electrometallurgy, in particular when making high-quality steels and alloys by the method of electroslag remelting.

Known in the prior art are methods of electroslag remelting of electrodes in a cooled mould with the use of a direct and alternating current, and installations for effecting said methods, in which the metal of the electrode, when passing dropwise through the layer of molten slag, is cleaned from non-metallic inclusions, the latter being absorbed by the slag. Besides, the metal drops, when forming and dropping, are subjected to a partial cleaning from sulphur, phosphorus and gases (see the book Electroslag remelting," by B.I.Medovar, Yu.V.Latash, Kiev, 1963, pp. 48 and 49).

It has been established that smaller drops of metal when passing through the layer of molten slag are likely to be cleaned quicker and more completely from non-metallic inclusions and other impurities than it is possible to achieve with larger drops.

I In the existing methods of electroslag remelting and the installations for efi'ecting same, the size of drops is determined by natural conditions of the melting process, the size of drops being sufficiently large, with the diameter ranging from 10 to 12 mm. For this reason, the exchange reactions occurring between the metal of the drop and the slag are insufiiciently vigorous, and the possibilities of the process of electroslag remelting are thus not completely used to advantage.

An object of the present invention is to eliminate the above said disadvantage.

The principal object of the present invention is to develop such ,an installation for electroslag remelting of consumable electrodes which would provide for amore complete cleaning of the metal being remelted from undesirable impurities owing to a considerable decrease in the size of drops of the electrode metal by way of positive breaking off of the drops prior to the moment of their being naturally broken off.

. 1 This object is accomplished, by superimposing short pulses of current on the working current of the electrode, the amplitude and duration of said pulses being fairly sufficient for the positive breaking off of the drops of electrode metal during the formation of the drop up to the moment of its being naturally broken off, which is taking place in the process of the electroslag remelting of consumable'electrodes in a cooled mould.

In conformity with the present invention, the installation for effecting the method described herein is provided with a pickup determining the moment of formation of the electrode metal drops, the input of said pickup being connected to a current measuring instrument, while its output is connected to a time relay actuating a control unit of the device setting up current pulses in the circuit of the consumable electrode.

In one of the embodiments of the installation for effecting the herein-described method, an ignitron contactor may be employed as the device for setting up current pulses in the circuit of the consumable electrode, said ignitron contactor being connected in series with a suitable source of current adapted to feed the circuit of the consumable electrode.

The nature of the present invention will become more fully apparent from a consideration of the following description of a preferred embodiment of the installation for electroslag remelting of consumable electrodes, taken in conjunction with the accompanying drawings illustrating one possible embodiment of the installation for effecting the proposed method, in which:

FIG. 1 represents a consumable electrode at the moment of a molten metal drop naturally breakingofi;

FIG. 2 shows the electrode at the moment when the drop of molten metal is positively broken off;

FIG. 3 represents an oscillogram of alternating current of the furnace with the natural breaking off of metal drops from the end of the consumable electrode;

FIG. 4 shows the oscillogram, with the positive breaking off of metal drops from the end of the consumable electrode;

FIG. 5 is a schematic diagram of the installation for the electroslag remelting effected according to the method of the invention; and

FIG. 6 represents an oscillogram of current, passing through the ignitron contactor of the proposed installation.

The essence of the proposed method is as follows. In the process of the electroslag remelting of consumable electrodes, the metal to be remelted is cleaned from undesirable impurities by making it interact with the molten slag. Among other factors, the degree of cleaning of the metal being remelted is determined by the magnitude of the surface of contact between the liquid metal and slag. A decrease in the size of drops signifies an increase in this surface, and is likely to speed up the processes of interaction of metal of the drop with the slag.

The liquid metal is retained at the electrode end by the force of surface tension F (FIG. 1) and hydrostatic lifting force F The force of gravity P and electrodynamic force F tend to separate the metal to be melted in the form of drops from the electrode end (FIG. 1). In the process of the electroslag remelting up to the moment of the natural breaking off of the metal drop, there is observed an inequality.

At the moment when the drop is naturally broken off, the forces tending to separate the drop from the end of the electrode (P F exceed the forces retaining the drop at the end of the electrode F F i.e., (P F (F F 2 Under the natural conditions of the melting process, this inequality is observed when the size of the drop is rather considerable (up to 10 to 12 mm. in diameter), mainly on account of an increase in the weight, and hence in the size of the drop.

The component of the electrodynamic force F compressing the electrode and tending to separate the molten metal therefrom, is directed downwards and proportional to the square of the current. When remelting withthe use of an alternating current, F varies with time according to the following law:

where o is the coefiicient of proportionality,

-r is the amplitude of alternating current,

w is the angular frequency of the current and t is the current moment of time.

From Equation (3) for the force F,,, it is evident that when remelting with the use of an alternating current of the angular frequency w, the force F is likely to preserve constant the direction of action, since cos 2wt=1, and varies from 0 to In order to decrease the size of drops of the electrode metal, i.e. to break ofi positively drops of small size, it is necessary, as it becomes evident from Equation (2), to increase for a short time the electrodynamic force F up to the value F (FIG. 2) which must be sufficient for effecting positive breaking off of the drop of electrode metal during the formation of the drop up to the moment of its natural breaking off.

An increase in the force F;, is achieved due to the superimposing of short pulses of current upon the working current of the furnace, the amplitude and duration of said current pulses being sufficient to effect the positive breaking off of small drops which is illustrated in FIGS. 3 and 4.

FIG. 3 shows an oscillogram of the alternating workingcurrent with the natural breaking off of drops of moltenmetal from the end of a consumable electrode. The current of frequency A equal to 50 cycles per-second, when passing through the electrode and melting down the slag, is modulated by the low frequency B. This is caused by the fact that the drop growing at the end of the electrode shunts the interelectrode gap, whose resistance determines the current of the furnace. Hence, on the oscillogram (FIG. 3) the minimum value of the amplitude of the working current 1', in each period T, corresponds to the absence of the drop at the end of the electrode, while the maximum value of the amplitude of the working current 1' corresponds to the moment immediately preceding the natural breaking ofi of the drop.

Thus, at each moment of time of each period the increment of the amplitude of the working current A 'r is determined from the equation:

A1- 1- 1', (4), where r is the value of the working current amplitude at a certain moment of time of the period under consideration;

1-, is the minimum value of current amplitude in the period under consideration, characterizing the size of the metal drop growing at the electrode end.

When Ar= A1, r 1,), there occurs natural breaking off of the drop from the end of the consumable electrode.

When remelting with the use of a direct current, the working current of the electrode is also likely to vary periodically as a result of shunting of the interelectrode gap by the drops of molten metal, and these variations of the working current during each period also characterize the size of the metal drop growing at the electrode end.

To effect positive breaking off of small drops of the electrode metal, pulses C of current (FIG. 4) are to be superimposed upon the working current, the current having the amplitude -rc 1' at the moments when O Ar AT (FIG. 4) An abrupt increase in the electrodynamic force F acting upon the molten metal at the electrode end, results in the positive breaking off of drops of molten metal. The magnitude of the pulse amplitude and duration T are to be selected for each particular case, on account of the complicated calculations required, so that said values be sufficient to effect positive breaking ofi of metal drops.

When comparing oscillograms represented in FIGS. 3 and 4, it becomes evident that the frequency of breaking off of metal drops when operating according to the proposed method is likely to increase, though the speed of the melting process remains constant, on account of which the surface of contact between the molten metal and liquid slag increases, which contributes to a more complete elimination of undesirable impurities from the metal being remelted.

One of the possible embodiments of the installation for effecting the proposed method of electroslag remelting of consumable electrodes is comprised of a furnace 2 (FIG. 5) for electroslag remelting with the use of an electrode 1 immersed into molten slag 3, a power transformer 4, an ignitron contactor 5, a unit 6 for controlling and igniting the ignitron of the ignitron contactor, a pickup 7 indicating the moment of formation of drops of the electrode metal, a current transformer 8, and a contactless time relay 9.

The installation represented in the drawing operates in the following manner: the ignitron contactor 5 is switched on and is operated by the unit 6 for controlling and igniting the ignitrons of the ignitron contactor in a continuous mode the ignition angle a (FIG. 6) equalling, for example, 70 to 90 and ensuring the working current of the furnace having the am plitude D. A signal from the current transfonner 8 is supplied to the pickup 7 indicating the moment of fonnation of the electrode metal drops.

At the moment 0 of beginning of the formation of the molten metal drop at the end of the electrode 1, as determined by the pickup 7 according to the value of the increment of the working current amplitude Ar 'r 1-,) (see Equation 4), a pulse C is produced at the output of the pickup 7, which is fed to the contactless time relay 9, synchronized with the network. The time relay 9 produces a rectangular pulse of a duration equal to one or a several periods of the supply network current, said pulse being fed to the unit 6 adapted for controlling and igniting the ignitrons of the ignitron contactor 5.

During the supply of the pulse C there occurs an abrupt variation of the ignition angle A i nitin the ignitrons from the working a 7 to 90) to the ull-p ase current a= 0),

There are also possible other embodiments of the installations for effecting the proposed method of electroslag remelting of consumable electrodes with the use of either alternating or direct current.

When carrying out the electroslag remelting according to the proposed method on the installation of the invention, there is achieved a considerable increase in the efficiency of treating metal with slag, owing to which the remelted metal possesses a lower percentage of sulphur, phosphorus, gases, non-metallic inclusions and other harmful impurities than it is possible to obtain by means of other known methods of electroslag remelting on the existing installations.

What is claimed is:

1. An installation for the electroslag remelting of consumable electrodes, comprising a furnace for remelting; a cooled mold connected to said furnace; an electric power means for feeding said furnace; a current measuring instrument; a device setting up impulses of current in the circuit of a consumable electrode; a means for controlling said device; a time relay acting upon said control unit; a pickup indicating the moment of the formation of drops of the electrode metal, the input into said pickup being connected to said current measuring instrument, while its output is connected to said time relay.

2. An installation as claimed in claim 1, wherein an ignitron contactor, connected in series with the current source for feeding the circuit of the consumable electrode, is employed as a device setting up impulses of current in the circuit of the consumable electrode.

3. An installation for electroslag remelting comprising: at least one consumable electrode, an electrode circuit for supplying working current from a current source to said electrode, a furnace having a cooled mold containing molten slag in which said electrode is melted, andpulse means for setting up current pulses in said electrode circuit in response to the formation of drops of the electrode metal, said pulse means including means for detecting the formation of drops of the electrode metal.

4. An installation as defined by claim 3, wherein said pulse means comprises a device for generating current pulses and a means for controlling said device.

5. An installation as defined by claim 4, wherein said means for detecting the formation of drops comprises a pickup means indicating the moment of the formation of drops of the electrode metal.

6. An installation as defined by claim 5, wherein a current measuring means provides the input to said pickup means.

7. An installation as defined by claim 4 wherein said device for generating current pulses comprises an ignitron contactor means connected in series with said current source for feeding said electrode circuit.

8. An installation as defined by claim 3 wherein said pulse means sets up current pulses in said electrode circuit sufficient for effecting positive break off of the drops of electrode metal prior to the time of their natural break off under the working current.

UN'E'IED STATES PATENT OFFICE CERTIFICATE 0i CCRRECTWN Patent No. 3 665 488 Dated May 23 1972 lnven fl Boris Evgenievich Paton et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the Title page, in the inventors names, change "Evgentevich" to -Evgenievich--.

Column 1, line 7, change "slag" to -electroslag--.

Column 2, line 4-, delete comma after "oscillogram".

, line 45, change "CW to -c'r line 48, change 'o" to- -c--.

Column 3, line 28, insert fieriod after (Fig. 4)

, line 56, insert comma after "rhode".

, line 69, delete "a".

Column 4, line 4, "A should be 1 4--,

Signed and sealed this 23rd day of January 1973* (SEAL) Attest:

EDWARD MZFLETCHERJR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PC4050 (w'ss) uscoMM-Dc scan-P09 US. GOVERNMENT PRINTING OFFICE Z "9 0-366-!" Um'mn STAEES lA'ilEN'l 0mm; CHERTWMATE 0t QQMHZQTWN Patent No. 3 665 4-88 I Dated May 23 1972 Inv nt Boris Evqenievich Paton et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the Title page, in the inventors names, change "Evgentevich" to --Evgenievich--.,

Column 1, line 7, change "slag" to --electroslag.

Column 2, line 4, delete comma after "oscillogram".

, line 45, change "CW to --c'r line 48, change 'o" to- -c--.

Column 3 line 28, insert Period after (Fig. 4) "o line 56, insert comma after "mode'k line 69, delete "a".,

Column 4, line 4, "A should be 0L Signed and sealed this 23rd day of January 1973 (SEAL) Attest:

EDWARD MZFLETCHERJR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-IOSO (10-69) USCOMM'DC 603764 69 U.5. GOVERNMENT PRINT NG OFFICE 2 I569 0-366-394 

1. An installation for the electroslag remelting of consumable electrodes, comprising a furnace for remelting; a cooled mold connected to said furnace; an electric power means for feeding said furnace; a current measuring instrument; a device setting up impulses of current in the circuit of a consumable electrode; a means for controlling said device; a time relay acting upon said control unit; a pickup indicating the moment of the formation of drops of the electrode metal, the input into said pickup being connected to said cuRrent measuring instrument, while its output is connected to said time relay.
 2. An installation as claimed in claim 1, wherein an ignitron contactor, connected in series with the current source for feeding the circuit of the consumable electrode, is employed as a device setting up impulses of current in the circuit of the consumable electrode.
 3. An installation for electroslag remelting comprising: at least one consumable electrode, an electrode circuit for supplying working current from a current source to said electrode, a furnace having a cooled mold containing molten slag in which said electrode is melted, and pulse means for setting up current pulses in said electrode circuit in response to the formation of drops of the electrode metal, said pulse means including means for detecting the formation of drops of the electrode metal.
 4. An installation as defined by claim 3, wherein said pulse means comprises a device for generating current pulses and a means for controlling said device.
 5. An installation as defined by claim 4, wherein said means for detecting the formation of drops comprises a pickup means indicating the moment of the formation of drops of the electrode metal.
 6. An installation as defined by claim 5, wherein a current measuring means provides the input to said pickup means.
 7. An installation as defined by claim 4 wherein said device for generating current pulses comprises an ignitron contactor means connected in series with said current source for feeding said electrode circuit.
 8. An installation as defined by claim 3 wherein said pulse means sets up current pulses in said electrode circuit sufficient for effecting positive break off of the drops of electrode metal prior to the time of their natural break off under the working current. 